Antenna system for defining glide paths



p 19430 L. .l. HEATON-ARMSTRONG 2, 9 I

ANTENNA SYS'I'EI FOR DEFINING GLIDE PATHS v Filed Oct. 15, 1943 2smug-sum 1 Inventor p 28, 1948. L. J. HEATON-ARMSTRONG 2,449,999

ANTENNA sxsml FOR DEFINING cubs PATHS Filed Oct. 15. 1943 2 Sh eets-Sheet a Invenlbr [oak Jain mhrpdnm/mz; y I I Patented Sept. 28, 1948ANTENNA SYSTEM FOR DEFINING GLIDE PATHS Louis John Keaton-Armstrong,London, England, assignor to Standard Telephones and Cables Limited,London, England, a British company 7 Application October 15, 1943,Serial No. 509,300

In Great Britain October 30, 1942 6 Claims. (Cl. 343108) The presentinvention relates to antenna systems for defining a radio glide path foraircraft and of the kind in which the glide path is defined by a line offield or signal strengths of constant relationship produced by twooverlapping fields in a vertical plane.

In one specific system one field comprises a plurality of directivelobes distributed angularly in a vertical plane and the other fieldcomprises a single principal lobe, the glide path being defined by theoverlapping of the lowermost lobe of the I multl-lobe pattern and singleprincipal lobe. The single principal lobe not only overlaps thelowermost lobe of the multi-lobe pattern but encloses the .second higherlobe of the multi-lobe pattern which is also of field strengthcomparable with the single principal lobe and it is found that the ratioof dot to dash signal strengths produced in a receiver suitably located,by the second lobe and single principal lobe is not as great asdesirable and in some cases might produce false constant radio orequi-signal glide paths.

The main object of the present invention is to provide an antenna systemfor defining a radio glide path in which these false courses are reducedor eliminated.

According to the present invention, in an antenna system for defining aradio glide path by a line of field or signal strengths of constantrelationship produced by two overlapping fields in a vertical plane andcomprising a first antenna unit The invention will be better understoodfrom the following description taken in conjunction with theaccompanying drawings, of one practical antenna system embodying. theinvention.

In the drawings,

Figure 1 shows an antenna system by which false glide paths areobtained.

Figure 2 shows the radiation patterns produced by the. antenna units ofthe arrangement shown in Figure 1.

Figure 3 shows the modification of one of the units according to thepresent invention, and

Figures 4, 5, 6 and 7 show field distribution patterns for differentconditions in the arrangement shown in Figure 3.

Referring to Figures 1 and 2 of thedrawings, the system for producing aglide path of the type hereinbefore specified comprises a horizontaldipole antenna i with parabolic reflector 2 located near to the groundto produce a distribution pattern having a principal lobe as shown atIn, Figure 2. Minor lobes approaching the vertical may also be presentbut these are not shown as they are not troublesome as regards thisinvention. The other antenna unit comprises also a horizontal dipole 3located before a plane reflector 4 so as to produce the multi-lobepattern as shown by the broken line H in Figure 2. The number of lobeswill depend, as is well known upon the height of the antenna 3 above theground.

The transmitter power is keyed from one antenna to the other in dot-dashrhythm thus producing an equi-slgnal path 0A, Figure 2, one of thesignals (dots or dashes) being received above 0A and the other signalbelow 0A. As already explained, since the lobe Iii encloses the secondhigher lobe i2, and the field strength of I0 is not very much greaterthan the field strength of i2, the-ratio between the dot and dashsignals of Ill and [2, produced by a receiver located within the lobesi9 and I2, is not sufi'iciently great for practical purposes and maylead to false glide paths. Likewise other lobes of the multi-lobepattern may produce with lobe I0, false paths. In the application of thepresent invention to this system, the dipole 3 is replaced by two dipoleantennae 5, 6 one above the other as shown in Figure 3. These twodipoles 5 and 6 are fed in phase and are separated by such a distance asto reduce or eliminate the lobes near the lowermost lobe i I.

In Figures 4, 5, 6 and 7 the energy distribution curves are shown infull lines for the upper antenna unit A, 5, 6 and in broken line for thelower antenna unit l, 2.

Figure 4 shows the case of a single antenna unit 3, 6 located at adistance above the ground equal to 7.2). (wave-lengths of the operatingfrequency).

Figures 5, 6 and '7 show corresponding diagrams for two antennae 5, 6,Figure 3, whose mean distance above the ground is 7.2x but havingdifferent separating distances of 3.2x, 3.87\ and 4.8x respectively.From these curves it is apparent that as the distance between theantennae 5 and 6 is increased, the second lobes marked B and higherlobes marked C become smaller, so that theratio 3 of desired toundesired signals above or below the glide path is increased.

It might of course be possible in some cases to provide an auxiliarydirective antenna system whose radiation pattern comprises a single lobewhich may be directed'in the same .direction as the lobe it is desiredto eliminate andied with current of the same frequency as the main unit3, d but so phased that the radiated fields of the auxiliary system andthe unit 4 are opposite in phase and keyed in the same manner andsynchronously with the lobe it is to eliminate or reduce.

Whilst a specific embodiment of the invention has been described it willbe understood that it is not limited to this embodiment but is capableof application to other systems utilising such radiation patterns asthose specified. Furthermore in the embodiment described, the distancebetween the two antennae, 5, B may be selected and the relativestrengths of currents fed to the two antennae adjusted accordinglyand/or the phase relationship of the currents fed to the two antennaemay be adjusted. Furthermore antenna systems other than the dipole andparabolic re= flector may be used for producing the single loberadiation pattern.

What is claimed is:

1. An antenna system for defining a glide path resulting from theover-lapping of two field patterns in a vertical plane, said antennacomprising. a first dipole antenna, a parabolic reflector for said firstantenna to provide a first antenna system having a vertical radiationpattern with a single principal lobe, a second dipole antenna disposedabove said first, a third dipole antenna disposed above said second,plane reflecting means for said second and third antennas to provide amulti-lobe vertical pattern, said principal lobe overlapping thelower-most lobe of said multilobe pattern, means for feeding said secondand third antennas in phase with each other, said second and thirdantennas together forming a composite antenna system having a meanheight above ground and having a separation between 4 the second andthird antenna of the order of one-half oi the mean height above groundwhereby the lobes due to the composite antenna system overlapped by theprincipal lobe of the first antenna system are substantially reduced.

2. The system oi claim 1 wherein said reflecting means for the secondand third antennas comprise a single plane reflector.

3. The system of claim 1 wherein the separation between the second andthird antennas is between three and live wave lengths.

4. The system of claim 1 wherein the average height above ground isseven plus a fraction of a wave length.

5. The system of claim 1 wherein the average height is 7.2 wave lengthsand wherein the separation between the second and third antennas isbetween three and live wave lengths.

6. The system of claim 1 wherein said reflecting means for the compositeantenna system is a single plane reflector, wherein the average heightabove ground is between seven and eight wave lengths of operatingfrequency and wherein the separation between the second and thirdantennas. is between three and five wave lengths.

LOUIS JOHN HEATON-ARMBTRONG.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,186,554 Pei-roux Jan. 9. 19402,189,283 Franz Feb. 6, 1949 2,213,859 Hahnemann Sept. 3, 1940 2,294,882Alford Sept. 8, 1942 FOREIGN PATENTS Number Country Date 23,158/35Australia July 2. 1936 438,900 Great Britain Nov. 26. 1935 546,021 GreatBritain June 24, 1942 556,824 Great Britain Sept. 29, 1943

